[cmd/opampsupervisor] Validate that the HUP config reload cannot be used on Windows (#41077)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

The changes in this PR add a validation in the Supervisor's agent
configuration that prevents the usage of the SIGHUP configuration reload
feature in Windows, as this OS doesn't support such signal.

This PR is a follow up to #40522. Thank you @nenadnoveljic for point it
out and notifying us of the Windows build failure.

<!--Describe what testing was performed and which tests were added.-->
#### Testing

Automated test added.

---------

Signed-off-by: Douglas Camata <[email protected]>

Author: douglascamata

cmd/opampsupervisor/supervisor/config/config.go

@@ -219,6 +219,10 @@ func (a Agent) Validate() error {
 		return errors.New("agent::config_apply_timeout must be valid duration")
 	}
 
+	if runtime.GOOS == "windows" && a.UseHUPConfigReload {
+		return errors.New("agent::use_hup_config_reload is not supported on Windows")
+	}
+
 	return nil
 }
 

cmd/opampsupervisor/supervisor/config/config_test.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"runtime"
 	"testing"
 	"time"
 
@@ -18,14 +19,20 @@ import (
 	"go.uber.org/zap/zapcore"
 )
 
+func simpleError(err string) func() string {
+	return func() string {
+		return err
+	}
+}
+
 func TestValidate(t *testing.T) {
 	tlsConfig := configtls.NewDefaultClientConfig()
 	tlsConfig.InsecureSkipVerify = true
 
 	testCases := []struct {
-		name          string
-		config        Supervisor
-		expectedError string
+		name              string
+		config            Supervisor
+		expectedErrorFunc func() string
 	}{
 		{
 			name: "Valid filled out config",
@@ -42,6 +49,7 @@ func TestValidate(t *testing.T) {
 					OrphanDetectionInterval: 5 * time.Second,
 					ConfigApplyTimeout:      2 * time.Second,
 					BootstrapTimeout:        5 * time.Second,
+					UseHUPConfigReload:      false,
 				},
 				Capabilities: Capabilities{
 					AcceptsRemoteConfig: true,
@@ -72,7 +80,7 @@ func TestValidate(t *testing.T) {
 					Directory: "/etc/opamp-supervisor/storage",
 				},
 			},
-			expectedError: "server::endpoint must be specified",
+			expectedErrorFunc: simpleError("server::endpoint must be specified"),
 		},
 		{
 			name: "Invalid URL",
@@ -96,7 +104,7 @@ func TestValidate(t *testing.T) {
 					Directory: "/etc/opamp-supervisor/storage",
 				},
 			},
-			expectedError: "invalid URL for server::endpoint:",
+			expectedErrorFunc: simpleError("invalid URL for server::endpoint:"),
 		},
 		{
 			name: "Invalid endpoint scheme",
@@ -120,7 +128,7 @@ func TestValidate(t *testing.T) {
 					Directory: "/etc/opamp-supervisor/storage",
 				},
 			},
-			expectedError: `invalid scheme "tcp" for server::endpoint, must be one of "http", "https", "ws", or "wss"`,
+			expectedErrorFunc: simpleError(`invalid scheme "tcp" for server::endpoint, must be one of "http", "https", "ws", or "wss"`),
 		},
 		{
 			name: "Invalid tls settings",
@@ -150,7 +158,7 @@ func TestValidate(t *testing.T) {
 					Directory: "/etc/opamp-supervisor/storage",
 				},
 			},
-			expectedError: "invalid server::tls settings:",
+			expectedErrorFunc: simpleError("invalid server::tls settings:"),
 		},
 		{
 			name: "Empty agent executable path",
@@ -175,7 +183,7 @@ func TestValidate(t *testing.T) {
 					Directory: "/etc/opamp-supervisor/storage",
 				},
 			},
-			expectedError: "agent::executable must be specified",
+			expectedErrorFunc: simpleError("agent::executable must be specified"),
 		},
 		{
 			name: "agent executable does not exist",
@@ -200,7 +208,7 @@ func TestValidate(t *testing.T) {
 					Directory: "/etc/opamp-supervisor/storage",
 				},
 			},
-			expectedError: "could not stat agent::executable path:",
+			expectedErrorFunc: simpleError("could not stat agent::executable path:"),
 		},
 		{
 			name: "Invalid orphan detection interval",
@@ -224,7 +232,7 @@ func TestValidate(t *testing.T) {
 					Directory: "/etc/opamp-supervisor/storage",
 				},
 			},
-			expectedError: "agent::orphan_detection_interval must be positive",
+			expectedErrorFunc: simpleError("agent::orphan_detection_interval must be positive"),
 		},
 		{
 			name: "Zero value health check port number",
@@ -297,7 +305,7 @@ func TestValidate(t *testing.T) {
 					Directory: "/etc/opamp-supervisor/storage",
 				},
 			},
-			expectedError: "agent::bootstrap_timeout must be positive",
+			expectedErrorFunc: simpleError("agent::bootstrap_timeout must be positive"),
 		},
 		{
 			name: "Invalid opamp server port number",
@@ -322,7 +330,7 @@ func TestValidate(t *testing.T) {
 					Directory: "/etc/opamp-supervisor/storage",
 				},
 			},
-			expectedError: "agent::opamp_server_port must be a valid port number",
+			expectedErrorFunc: simpleError("agent::opamp_server_port must be a valid port number"),
 		},
 		{
 			name: "Zero value opamp server port number",
@@ -371,7 +379,38 @@ func TestValidate(t *testing.T) {
 					Directory: "/etc/opamp-supervisor/storage",
 				},
 			},
-			expectedError: "agent::config_apply_timeout must be valid duration",
+			expectedErrorFunc: simpleError("agent::config_apply_timeout must be valid duration"),
+		},
+		{
+			name: "HUP config reload not supported on Windows",
+			config: Supervisor{
+				Server: OpAMPServer{
+					Endpoint: "wss://localhost:9090/opamp",
+					Headers: http.Header{
+						"Header1": []string{"HeaderValue"},
+					},
+					TLS: tlsConfig,
+				},
+				Agent: Agent{
+					Executable:              "${file_path}",
+					OrphanDetectionInterval: 5 * time.Second,
+					ConfigApplyTimeout:      2 * time.Second,
+					BootstrapTimeout:        5 * time.Second,
+					UseHUPConfigReload:      true,
+				},
+				Capabilities: Capabilities{
+					AcceptsRemoteConfig: true,
+				},
+				Storage: Storage{
+					Directory: "/etc/opamp-supervisor/storage",
+				},
+			},
+			expectedErrorFunc: func() string {
+				if runtime.GOOS != "windows" {
+					return ""
+				}
+				return "agent::use_hup_config_reload is not supported on Windows"
+			},
 		},
 	}
 
@@ -394,10 +433,10 @@ func TestValidate(t *testing.T) {
 
 			err := tc.config.Validate()
 
-			if tc.expectedError == "" {
-				require.NoError(t, err)
+			if tc.expectedErrorFunc != nil && tc.expectedErrorFunc() != "" {
+				require.ErrorContains(t, err, tc.expectedErrorFunc())
 			} else {
-				require.ErrorContains(t, err, tc.expectedError)
+				require.NoError(t, err)
 			}
 		})
 	}